FIG. 1 is a schematic illustration of a network 1 that allows wireless communication with a mobile device 5. The mobile device may be, for example, a mobile telephone or a handheld wireless device such as a BlackBerry™ device and will be referred to generally as a “mobile node” (MN).
As is well known, a mobile node 5 may connect to the network 1 via one of a plurality of access points 4 (“AP”). Each access point has a defined area of geographic coverage and, as the mobile node 5 moves, it is “handed-off” from one access point to another when it passes from a geographic area served by one access point to the geographic area served by another access point. It is desirable that the user of the mobile node does not experience any breakdown or interruption in communication when the mobile node is handed-off from one access point to another.
Network-based Local Mobility Management (NetLMM) is an IETF endorsed approach to provide mobile nodes with an illusion of an extended layer 2 link. One specific solution to the NetLMM problem is currently being standardised in the NETLMM working group at the IETF. The basic architecture, as being worked on at the IETF, is presented in FIG. 1 and is described by H. Levkowetz, Editor, et al., in “The NetLMM Protocol”, Internet draft draft-giaretta-netlmm-dt-protocol-02, work in progress, October 2006.
In the network of FIG. 1, a number of Access Routers (ARs) 3a,3b,3c, also called Mobile Access Gateways (MAG), participate in a NetLMM domain. The Access Routers of an NetLMM domain are associated with a Local Mobility Anchor 2a,2b; in the example of FIG. 1 the Access Routers 3a,3b participate in one NetLMM domain associated with one Local Mobility Anchor 2a, whereas the Access Router 3c participates in a different NetLMM domain associated with another Local Mobility Anchor 2b. The Access Routers in one NetLMM domain all announce the same IPv6 routing prefix in their Neighbour Discovery Protocol (NDP) Router Advertisement (RA) messages. This creates the illusion that the same IPv6 link is extended between these ARs, therefore avoiding the need for any explicit mobility signalling between the mobile node and the NetLMM domain as long as the mobile node remains in that NetLMM domain. In other words, the mobile node preserves its IP address as long as its mobility is confined within the NetLMM domain. In FIG. 1, a mobile node that moves between one Access Point controlled by an Access Router and another Access Point controlled by the same Access Router (denoted by “Intra-Link Mobility” in FIG. 1) or a mobile node that moves between one Access Point controlled by an Access Router and another Access Point controlled by another Access Router but associated with the same Local Mobility Anchor as the first Access Router (denoted by “Local Mobility” in FIG. 1) remains in one NetLMM domain. However, a Mobile Node that moves between one Access Point controlled by an Access Router associated with one Local Mobility Anchor to another Access Point controlled by an Access Router associated with another Local Mobility Anchor (denoted by “Global Mobility” in FIG. 1) moves from one NetLMM domain to another NetLMM domain.